A voltage regulator is an electronic device that compares an input voltage with a reference voltage to generate an output at a selected voltage level. Voltage regulators can be used in many circuit applications that require a constant level of power supply. One of such applications can be a probe card assembly interfacing between at least one tester and one or more devices under test (DUTs), which may be, for example, one or more dies of a semiconductor wafer, one or more singulated semiconductor dies of an array of dies, or any other electronic device or devices. The probe card assembly can include a plurality of probes with electrical and mechanical characteristics capable of forming resilient pressure contacts with a plurality of terminals of DUTs to send and/or receive signals to/from the DUTs. The probe card assembly can also include a number of connectors adapted to be connected to a tester via one or more communication links. The probe card assembly can be embedded with wirings connecting the connectors on one side and the probes on the other side. Thus, when the tester is connected to the probe card assembly and the probes are brought in contact with the terminals of DUTs, the tester can transmit testing signals to the DUTs and receive resulting signals therefrom. The tester can analyze the received resulting signals to determine whether any of the DUTs is defective.
FIG. 1A illustrates a system 100 in which a probe card assembly 106 is connected to a tester 102 via a communication link 108. The probe card assembly 106 can include a number of voltage regulators VR1, . . . and VRn connected to a number of DUTs (DUT1, . . . and DUTn, where n can range from 1 to a number greater than 1) via a number of test channels CH1, . . . and CHn, respectively. Each of the test channels CH1, . . . and CHn can include, among other things, a probe in contact with a terminal of each DUT (physical structures of the probes and the terminals are not shown in this figure). The voltage regulators VR1, . . . and VRn can receive power inputs from a power supply (not shown) in the tester 102, and generate power outputs at a selected voltage level to their corresponding DUTs (DUT1, . . . and DUTn). The voltage regulators VR1, . . . and VRn are often current limited, so that a defective DUT that draws a large amount of current would not significantly affect the current supply for other functional DUTs. Oftentimes, the tester is required to program the voltage regulators to output a selected voltage. This programming can require a number of control channels.
FIG. 1B schematically illustrates a conventional voltage regulator 110 adapted to be used as the voltage regulators VR1, . . . and VRn employed in the system 100 shown in FIG. 1A. The voltage regulator 110 can include a variable switch 112 and a controller 114. The variable switch 112 can receive a power input Vin from a power supply, and generate a power output Vout at a selected voltage level. The controller 114 can receive a sense signal Vsense indicating a voltage level of the power output Vout, and compare it with a reference voltage Vref to generate a control signal based on the voltage difference between the sense signal Vsense and the reference voltage Vref. The greater the difference between the sense signal Vsense and the reference voltage Vref, the more or less the variable switch 112 is turned on. When the variable switch 112 and the controller 114 are in equilibrium, the voltage level of the sense signal Vsense (hence, the voltage level of the power output Vout) would become equal a value proportional to the reference voltage Vref, thereby controlling the power output Vout of the variable switch 112 at a selected, predetermined level.
Conventionally, the voltage level of the reference voltage Vref is not sensitive to that of the power input Vin. The reference voltage Vref is adjusted independently from the power input Vin in order to alter the power output Vout. In the context where the voltage regulator 110 is employed in an apparatus such as the test system 100 shown in FIG. 1A, the reference voltages of voltage regulators VR1, . . . and VRn need to be programmed individually and independently by digital or analog methods in order to ensure all the power outputs from the voltage regulators VR1, . . . and VRn to be at a predetermined voltage level. If the predetermined voltage level were to be changed, all of the voltage regulators VR1, . . . and VRn would need to be reprogrammed individually and independently. Such reprogramming requires complex circuit designs to implement a digital or analog control scheme over the voltage regulators. In case where those voltage regulators are implemented in a probe card assembly, the complex circuit design requirements can increase the costs of designing and fabricating the probe card assembly significantly. Such reprogramming can also be time-consuming and prone to errors. As a result, such reprogramming can prolong the time required to ready the probe card assembly to perform tests, thereby increasing the tested per unit time of each DUT.